With the development of mobile communications, a series of miniaturized base stations are introduced, which include a femtocell, a picocell, a metrocell, a microcell, and the like, and these technologies may be collectively referred to as small cells.
In a small cell, to satisfy requirements of instantaneous uplink and downlink service volume, a flexible subframe may be introduced, and each flexible subframe may be dynamically configured to be an uplink subframe or a downlink subframe. In the small cell, a fake uplink subframe may be introduced, in other words, no uplink data is sent in the subframe. In the small cell, to match a service requirement and an interference change, a user equipment (UE) may rapidly switch between different carriers. In the small cell, a UE that has only a single uplink transmit chain capability may communicate with different base stations, and the different base stations exchange information by using non-ideal backhaul.
Currently, in a Long Term Evolution (LTE) system, uplink and downlink hybrid automatic repeat request (HARQ) feedback, in other words, an acknowledgement (ACK) or a non-acknowledgement (NACK) (hereinafter referred to as ACK/NACK for short), is sent according to a fixed time sequence relationship.
Because the new technologies are introduced into the small cell, if the HARQ feedback sent according to the fixed sequential relationship in the LTE is still used in the small cell, the use of the flexible subframe, the fake uplink subframe, and rapid carrier switching are limited, and the UE with the single uplink transmit chain capability cannot be well supported. Therefore, to support the new technologies in the small cell more effectively, a current HARQ mechanism needs to be improved.